While it is well known to utilize reinforcing elements including various types of fibers to provide increased strength in paper products, the known fibrous materials do not impart much in the way of structural strength, nor do they add much rigidity and stiffness to the finished product. In the case of corrugated board, which is made with various weights of paper, increased stiffness and strength have been obtained by increasing the weight of the paper utilized for both the corrugated central medium as well as the overlying layers or facings. In fact, when heavy packing cases were to be made of corrugated board, several layers of corrugated board had to be laminated in order to obtain the desired stiffness and strength. It is well known that corrugated board has been manufactured for many decades, yet the only procedures that have been considered economical and practical to obtain increased structural strength and stiffness have involved the use of paper of increased weight, and the lamination of layers of corrugated board. It is well recognized however that notwithstanding the utilization of heavier paper, and also the lamination of corrugated board that the resulting product is still subject to adverse effects of moisture which results in substantial softening of the board and loss of the protection intended to be afforded by it. Furthermore, to waterproof the resulting cardboard structure to eliminate the adverse effects of moisture it has thus far been necessary to wax the cardboard or to cover the interior of the cardboard with a polyurethane film.
In copending Application Ser. No. 599,142, filed July 25, 1975, for "Reinforced Paper Products and Method and Apparatus for the Manufacturing Thereof," there is disclosed an improved wire reinforced corrugated board and other products in which the corrugated medium for corrugated board is comprised of a plurality of wires adhered in firm contact to a paper web which is then corrugated transversely of the wires so that the wires and the paper conform to one another. This corrugated medium then has outer paper layers or liners adhered to the crest portions of each side of the corrugating medium to form a double faced wire reinforced corrugated board. The plurality of wire elements in the corrugating medium provide improved rigidity and strength for the resulting corrugated board. In particular, the compressive or bending forces applied to the corrugated board are greatly increased as a result of the triangular truss structure formed by the wire elements in the corrugating medium of a double-faced cardboard construction. That is, when compressive or bending forces are applied to the cardboard, the wire legs are placed into compression which is one of the strengths of wire. Thus, the structure will support substantial compressive forces.
In that copending application, the wires were adhered onto the surface of a single paper web before corrugation. Further, an overlying paper web could be adhered on top of the wires so that the wires were completely enclosed in a paper structure. Due to the thinness of the paper webs and the thickness of the wires positioned therebetween, and to the fact that it is desired that the two paper webs be adhered to one another, a series of ridges were produced on at least one of the outer surfaces of the paper structure. It may be desired, for a variety of reasons, to eliminate these ridges. For example, a smooth outer surface would both be aesthetically pleasing as well as easier to be adhered to. Further, as can be appreciated, when wires are only placed on the surface between the two layers, great care is necessary to insure that the two paper webs are securely adhered together.